Subject: CVE-2024-40949: mm: shmem: fix getting incorrect lruvec when replacing a shmem folio

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

mm: shmem: fix getting incorrect lruvec when replacing a shmem folio

When testing shmem swapin, I encountered the warning below on my machine. 
The reason is that replacing an old shmem folio with a new one causes
mem_cgroup_migrate() to clear the old folio's memcg data.  As a result,
the old folio cannot get the correct memcg's lruvec needed to remove
itself from the LRU list when it is being freed.  This could lead to
possible serious problems, such as LRU list crashes due to holding the
wrong LRU lock, and incorrect LRU statistics.

To fix this issue, we can fallback to use the mem_cgroup_replace_folio()
to replace the old shmem folio.

[ 5241.100311] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5d9960
[ 5241.100317] head: order:4 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 5241.100319] flags: 0x17fffe0000040068(uptodate|lru|head|swapbacked|node=0|zone=2|lastcpupid=0x3ffff)
[ 5241.100323] raw: 17fffe0000040068 fffffdffd6687948 fffffdffd69ae008 0000000000000000
[ 5241.100325] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 5241.100326] head: 17fffe0000040068 fffffdffd6687948 fffffdffd69ae008 0000000000000000
[ 5241.100327] head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 5241.100328] head: 17fffe0000000204 fffffdffd6665801 ffffffffffffffff 0000000000000000
[ 5241.100329] head: 0000000a00000010 0000000000000000 00000000ffffffff 0000000000000000
[ 5241.100330] page dumped because: VM_WARN_ON_ONCE_FOLIO(!memcg && !mem_cgroup_disabled())
[ 5241.100338] ------------[ cut here ]------------
[ 5241.100339] WARNING: CPU: 19 PID: 78402 at include/linux/memcontrol.h:775 folio_lruvec_lock_irqsave+0x140/0x150
[...]
[ 5241.100374] pc : folio_lruvec_lock_irqsave+0x140/0x150
[ 5241.100375] lr : folio_lruvec_lock_irqsave+0x138/0x150
[ 5241.100376] sp : ffff80008b38b930
[...]
[ 5241.100398] Call trace:
[ 5241.100399]  folio_lruvec_lock_irqsave+0x140/0x150
[ 5241.100401]  __page_cache_release+0x90/0x300
[ 5241.100404]  __folio_put+0x50/0x108
[ 5241.100406]  shmem_replace_folio+0x1b4/0x240
[ 5241.100409]  shmem_swapin_folio+0x314/0x528
[ 5241.100411]  shmem_get_folio_gfp+0x3b4/0x930
[ 5241.100412]  shmem_fault+0x74/0x160
[ 5241.100414]  __do_fault+0x40/0x218
[ 5241.100417]  do_shared_fault+0x34/0x1b0
[ 5241.100419]  do_fault+0x40/0x168
[ 5241.100420]  handle_pte_fault+0x80/0x228
[ 5241.100422]  __handle_mm_fault+0x1c4/0x440
[ 5241.100424]  handle_mm_fault+0x60/0x1f0
[ 5241.100426]  do_page_fault+0x120/0x488
[ 5241.100429]  do_translation_fault+0x4c/0x68
[ 5241.100431]  do_mem_abort+0x48/0xa0
[ 5241.100434]  el0_da+0x38/0xc0
[ 5241.100436]  el0t_64_sync_handler+0x68/0xc0
[ 5241.100437]  el0t_64_sync+0x14c/0x150
[ 5241.100439] ---[ end trace 0000000000000000 ]---

[[email-masked]: remove less helpful comments, per Matthew]
  Link: https://lkml.kernel.org/r/cca[email-masked]

The Linux kernel CVE team has assigned CVE-2024-40949 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.7 with commit 85ce2c517ade and fixed in 6.9.7 with commit 8c6c3719ebb7
	Issue introduced in 6.7 with commit 85ce2c517ade and fixed in 6.10 with commit 9094b4a1c76c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-40949
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/memcontrol.c
	mm/shmem.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8c6c3719ebb7913f8a665d11816d2e38b0eadbab
	https://git.kernel.org/stable/c/9094b4a1c76cfe84b906cc152bab34d4ba26fa5c